Studies on the molecular biology of SV40 virus multiplication and oncogenesis will be continued with particular emphasis on the following projects: l. Isolation and characterization of SV40 DNA molecules containing deletions and substitutions and to correlate these modifications with the alterations in the phenotype. 2. Characterization of the chromatin-like form of intranuclear SV40 DNA with respect to the types of protein and their arrangement on the DNA. 3. Use of restriction endonucleases to dissect the SV40 DNA molecule and to construct modified genomes for physical and genetic studies. 4. Analysis of the mechanism of integration of SV40 DNA into cellular and other viral DNAs and characterization of the integrated mode.